Known dialysis machines normally comprise a blood circulating circuit connected, in use, to the patient's circulatory system; a treatment fluid circulating circuit; and a filter, through which the blood circulating circuit feeds the blood, and the treatment fluid circulating circuit feeds the treatment fluid. The filter comprises a semipermeable membrane for separating, in use, the treatment fluid from the blood, so that ions are exchanged between the treatment fluid and the blood, and part of the plasma in the blood is transferred through the membrane. The blood circulating circuit comprises an arterial branch upstream from the filter, and a venous branch downstream from the filter, and the machine comprises a peristaltic pump located along the arterial branch to feed the patient's blood to the filter. The blood circulating circuit and second the treatment fluid circulating circuit are made of transparent, flexible material, such as PVC, which ensures sterility of the circuits. The flexibility of the circuits simplifies packaging and enables flow to be cut off by simply constricting a portion of the circuit, while transparency enables visual monitoring of liquid flow in the circuit.
During the dialysis treatment itself, certain physical characteristics of the blood along the first circuit are determined non-invasively to monitor treatment and possibly also adjust dialysis parameters. This is normally done by means of pressure sensors and sensors for detecting the absorption of electromagnetic waves by the blood. Such sensors are provided on the dialysis machine and are connected to specific points along the first circuit, which is used for one dialysis treatment only and then disposed of as controlled waste.